The constellation Lyra stands high overhead as darkness falls this evening. Its most prominent feature is Vega, one of the brightest stars in the night sky.

Through a telescope, though, one of the harp's most impressive features is the Ring Nebula -- a shell of gas expelled by a dying star. Today, we know that such nebulae consist of the same elements found on Earth. But in the past, some scientists thought otherwise.

In the nineteenth century, astronomers first measured light from nebulae at specific wavelengths. Scientists saw some of the same patterns of light in the laboratory, and deduced that the light from the nebulae was produced by the same chemical elements as those in the lab.

But other patterns were puzzling. For example, nebulae often glowed brightly at two green wavelengths. No one had ever seen this in the laboratory. So some scientists thought nebulae harbored a new element: nebulium. In the same way, scientists had first detected a new element on the Sun and named it helium, for the Greek Sun god Helios.

But while helium is a real element, nebulium is not. In the 1920s, scientists realized that the mysterious green color came not from an exotic element, but from one of the most familiar: oxygen. In the extreme conditions of space, oxygen atoms do things they almost never do on Earth, producing the unearthly light.

So nebulium -- which had seemed so alien and exotic -- turned out instead to be quite ordinary and down-to-earth.